theorem :: COHSP_1:43

for C1, C2 being Coherence_Space
for a being Element of C1
for y being set
for f being U-stable Function of C1,C2 st Trace f = {[a,y]} holds
for b being Element of C1 holds
( ( a c= b implies f . b = {y} ) & ( not a c= b implies f . b = {} ) )