theorem Th37: :: CAT_4:37

for C being Cartesian_category
for a, b, c being Object of C holds
( (Alpha (a,b,c)) * (Alpha' (a,b,c)) = id (a [x] (b [x] c)) & (Alpha' (a,b,c)) * (Alpha (a,b,c)) = id ((a [x] b) [x] c) )