FA-88211 / Inverse kinematics solvers / Open access
Negative elbow angles are treated as singular · case 01
Every elbow-down pose is damped as if it sat on the singularity.
ROOT CAUSE
The manipulability drops the absolute value, so negative sin q2 falls below the threshold.
VERIFIED REPAIR
Take the absolute value of l1 l2 sin q2.
Unsuccessful approach: Squaring the measure compares a squared quantity with an unsquared threshold.
Case contract
Input [l1,l2,q1,q2,vx,vy,w0,lam0]: resolved-rate step for a planar 2R arm. Manipulability w=|l1 l2 sin q2|. Damping lam^2 = 0 when w>=w0, else lam0^2 (1-w/w0)^2. Solve (J^T J + lam^2 I) qdot = J^T v; if that matrix determinant is below 1e-12 return ["singular", w]. Return [status, qdot1, qdot2] in degrees per second, status "damped" when lam^2>0 else "exact".
Why this case matters
Inverse kinematics code turns task-space goals into joint commands; a wrong branch, sign, limit or update order sends a real arm to the wrong pose.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
l1,l2,q1,q2,vx,vy,w0,lam0=x
a=math.radians(q1)
b=math.radians(q1+q2)
J=[[-l1*math.sin(a)-l2*math.sin(b),-l2*math.sin(b)],[l1*math.cos(a)+l2*math.cos(b),l2*math.cos(b)]]
w=l1*l2*math.sin(math.radians(q2))
lam2=0.0 if w>=w0 else lam0*lam0*(1.0-w/w0)**2
m11=J[0][0]**2+J[1][0]**2+lam2
m12=J[0][0]*J[0][1]+J[1][0]*J[1][1]
m22=J[0][1]**2+J[1][1]**2+lam2
det=m11*m22-m12*m12
if det<1e-12: return ['singular',round(w,6)]
g1=J[0][0]*vx+J[1][0]*vy
g2=J[0][1]*vx+J[1][1]*vy
d1=(m22*g1-m12*g2)/det
d2=(-m12*g1+m11*g2)/det
return ['damped' if lam2>0 else 'exact',round(math.degrees(d1),4),round(math.degrees(d2),4)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]], ['mid zone', [[1.5, 1, 20, 12, 0.0, -0.2, 0.6, 0.25]], ['damped', -11.2758, 17.8448]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]]]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| well conditioned | ['exact', 7.0591, -17.7507] | ['exact', 7.0591, -17.7507] | Passed |
| near singular damped | ['damped', 11.4896, -16.5029] | ['damped', 11.4896, -16.5029] | Passed |
| negative elbow near singular | ['damped', 0.3661, 6.7816] | ['damped', -5.2725, 18.1241] | Failed |
| negative elbow well conditioned | ['damped', 2.0937, -6.4982] | ['exact', 9.4468, -19.8957] | Failed |
| straight arm damped | ['damped', 6.8209, 3.4105] | ['damped', 6.8209, 3.4105] | Passed |
| straight arm undamped | ['singular', 0.0] | ['singular', 0.0] | Passed |
| inside zone no damping gain | ['exact', 10.8225, -34.1537] | ['exact', 10.8225, -34.1537] | Passed |
SHA-256 / 9a2950bc2522e63dc7d9e3ef6471765d4de31297b923b99d95a2f92e84dab916
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
l1,l2,q1,q2,vx,vy,w0,lam0=x
a=math.radians(q1)
b=math.radians(q1+q2)
J=[[-l1*math.sin(a)-l2*math.sin(b),-l2*math.sin(b)],[l1*math.cos(a)+l2*math.cos(b),l2*math.cos(b)]]
w=(l1*l2*math.sin(math.radians(q2)))**2
lam2=0.0 if w>=w0 else lam0*lam0*(1.0-w/w0)**2
m11=J[0][0]**2+J[1][0]**2+lam2
m12=J[0][0]*J[0][1]+J[1][0]*J[1][1]
m22=J[0][1]**2+J[1][1]**2+lam2
det=m11*m22-m12*m12
if det<1e-12: return ['singular',round(w,6)]
g1=J[0][0]*vx+J[1][0]*vy
g2=J[0][1]*vx+J[1][1]*vy
d1=(m22*g1-m12*g2)/det
d2=(-m12*g1+m11*g2)/det
return ['damped' if lam2>0 else 'exact',round(math.degrees(d1),4),round(math.degrees(d2),4)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]], ['mid zone', [[1.5, 1, 20, 12, 0.0, -0.2, 0.6, 0.25]], ['damped', -11.2758, 17.8448]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]]]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| well conditioned | ['exact', 7.0591, -17.7507] | ['exact', 7.0591, -17.7507] | Passed |
| near singular damped | ['damped', 7.4564, -8.4624] | ['damped', 11.4896, -16.5029] | Failed |
| negative elbow near singular | ['damped', -1.5284, 10.6119] | ['damped', -5.2725, 18.1241] | Failed |
| negative elbow well conditioned | ['exact', 9.4468, -19.8957] | ['exact', 9.4468, -19.8957] | Passed |
| straight arm damped | ['damped', 6.8209, 3.4105] | ['damped', 6.8209, 3.4105] | Passed |
| straight arm undamped | ['singular', 0.0] | ['singular', 0.0] | Passed |
| inside zone no damping gain | ['exact', 10.8225, -34.1537] | ['exact', 10.8225, -34.1537] | Passed |
SHA-256 / 5cd8b20d9401c9453b41afd05d474f8b6e8cc9af0599b19e3a7627009c0bef13
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
import math
N = 1
observations = []
def solve(x):
l1,l2,q1,q2,vx,vy,w0,lam0=x
a=math.radians(q1)
b=math.radians(q1+q2)
J=[[-l1*math.sin(a)-l2*math.sin(b),-l2*math.sin(b)],[l1*math.cos(a)+l2*math.cos(b),l2*math.cos(b)]]
w=abs(l1*l2*math.sin(math.radians(q2)))
lam2=0.0 if w>=w0 else lam0*lam0*(1.0-w/w0)**2
m11=J[0][0]**2+J[1][0]**2+lam2
m12=J[0][0]*J[0][1]+J[1][0]*J[1][1]
m22=J[0][1]**2+J[1][1]**2+lam2
det=m11*m22-m12*m12
if det<1e-12: return ['singular',round(w,6)]
g1=J[0][0]*vx+J[1][0]*vy
g2=J[0][1]*vx+J[1][1]*vy
d1=(m22*g1-m12*g2)/det
d2=(-m12*g1+m11*g2)/det
return ['damped' if lam2>0 else 'exact',round(math.degrees(d1),4),round(math.degrees(d2),4)]
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['inside zone no damping gain', [[1, 1, 45, 10, 0.2, -0.1, 0.5, 0.0]], ['exact', 10.8225, -34.1537]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]]], [['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['folded arm', [[1, 1, 60, 175, 0.05, 0.05, 0.2, 0.1]], ['damped', -32.2582, 0.8237]], ['long links', [[2, 1.5, -20, 40, 0.3, 0.3, 0.5, 0.3]], ['exact', 17.1371, -27.792]], ['exact threshold', [[1, 2, 10, 30, 0.1, 0.1, 1.0, 0.4]], ['damped', 16.144, -22.7815]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['large damping', [[1, 1, 90, 8, -0.1, 0.0, 0.8, 0.6]], ['damped', 2.2347, 0.9844]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]], ['small straight damping', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0002]], ['damped', 6.8755, 3.4377]], ['mid zone', [[1.5, 1, 20, 12, 0.0, -0.2, 0.6, 0.25]], ['damped', -11.2758, 17.8448]]], [['well conditioned', [[1, 1, 30, 90, 0.1, 0.2, 0.3, 0.2]], ['exact', 7.0591, -17.7507]], ['near singular damped', [[1, 1, 30, 5, 0.1, 0.2, 0.3, 0.2]], ['damped', 11.4896, -16.5029]], ['negative elbow near singular', [[1, 1, 30, -5, 0.1, 0.2, 0.3, 0.2]], ['damped', -5.2725, 18.1241]], ['negative elbow well conditioned', [[1, 1, 10, -80, -0.2, 0.1, 0.3, 0.2]], ['exact', 9.4468, -19.8957]], ['straight arm damped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.2]], ['damped', 6.8209, 3.4105]], ['straight arm undamped', [[1, 1, 0, 0, 0.0, 0.3, 0.3, 0.0]], ['singular', 0.0]], ['slightly above threshold', [[1, 1, 0, 20, 0.2, 0.2, 0.3, 0.5]], ['exact', 42.9429, -76.4473]]]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| well conditioned | ['exact', 7.0591, -17.7507] | ['exact', 7.0591, -17.7507] | Passed |
| near singular damped | ['damped', 11.4896, -16.5029] | ['damped', 11.4896, -16.5029] | Passed |
| negative elbow near singular | ['damped', -5.2725, 18.1241] | ['damped', -5.2725, 18.1241] | Passed |
| negative elbow well conditioned | ['exact', 9.4468, -19.8957] | ['exact', 9.4468, -19.8957] | Passed |
| straight arm damped | ['damped', 6.8209, 3.4105] | ['damped', 6.8209, 3.4105] | Passed |
| straight arm undamped | ['singular', 0.0] | ['singular', 0.0] | Passed |
| inside zone no damping gain | ['exact', 10.8225, -34.1537] | ['exact', 10.8225, -34.1537] | Passed |
SHA-256 / 6e9985182e462982f02d273034a87899e4141ab3d1901faa733bd5030b09f764
Verification & scope
Deterministic planar or low-dimensional teaching model with a stipulated convention; not a general robotics library. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:51:06.077699+00:00.
Case digest / 9c51684b005ca70d41e4acfb33b6657b3932809894b871987103bd423913d151