Semigroup

$\textbf{Semigroup} \; A \; \otimes$

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$\textbf{Magma} \; A \; \otimes$

$\forall(x,y,z \in X : (x \otimes y) \otimes z = x \otimes (y \otimes z))$

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pred Semigroup(A: set univ, op: univ->univ->univ) {
  Magma[A,op]
  all x,y,z: A | op[op[x,y],z] = op[x,op[y,z]]
}