User:Dfeuer/Definition:Cone Compatible with Operation
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Definition
Let $\struct {S, \circ}$ be a magma.
Let $C$ be a subset of $S$.
Suppose that for each $x,y \in S$:
- $(1): \quad$ If $x, y \in C$ then $x \circ y \in C$
- $(2): \quad$ If $x \circ y \in C$ then $y \circ x \in C$.
Then $C$ is a cone compatible with $\circ$.
Note that the second condition is trivially satisfied when $\circ$ is commutative, as when it is the operation of an abelian group or the addition operation of a ring.