}       {\alpha^M : A * M * B {\ensuremath{\xymatrix@0@C=00pt{\ar[r]&}}}M}$$ Composition of morphisms $M: \xymatrix@0@C=00pt{A \ar[r] |-{\object@{|}} & B}$ and $N: \xymatrix@0@C=00pt{B \ar[r] |-{\object@{|}} & C}$ is 