theorem Th136: :: ZMODUL01:136

for R being Ring
for V being LeftMod of R
for W1, W2 being Submodule of V
for v being Vector of V st V is_the_direct_sum_of W1,W2 holds
(v |-- (W1,W2)) `1 = (v |-- (W2,W1)) `2 by VECTSP_5:50;