===== Binary function =====
==== Set ====
| @#55CCEE: context     | @#55CCEE: $X,Y$ |

| @#FFBB00: definiendum | @#FFBB00: $ f\in \text{it}(X,Y) $ |

| @#55EE55: postulate   | @#55EE55: $ f:X\times X\to Y $ | 

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=== Subset of ===
[[Function]]