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| Picture an arbitrary function from a ''source'' or ''domain'' to a ''target'' or ''codomain''. Here is a picture of such function, <math>f : X \to Y,</math> as generic as it needs to be for our prsent purposes: | | Picture an arbitrary function from a ''source'' or ''domain'' to a ''target'' or ''codomain''. Here is a picture of such function, <math>f : X \to Y,</math> as generic as it needs to be for our prsent purposes: |
| | | |
| + | {| align="center" cellpadding="10" style="text-align:center; width:90%" |
| + | | |
| <pre> | | <pre> |
− | Source X = {1, 2, 3, 4, 5}
| + | o---------------------------------------o |
− | | o o o o o
| + | | | |
− | f | \ | / \ /
| + | | Source X = {1, 2, 3, 4, 5} | |
− | | \|/ \ /
| + | | | o o o o o | |
− | v o o o o o o
| + | | f | \ | / \ / | |
− | Target Y = {A, B, C, D, E, F}
| + | | | \|/ \ / | |
| + | | v o o o o o o | |
| + | | Target Y = {A, B, C, D, E, F} | |
| + | | | |
| + | o---------------------------------------o |
| </pre> | | </pre> |
| + | |} |
| | | |
| It is a fact that any old function that you might pick "factors" into a functional composition of two other functions, a surjective ("onto") function and an injective ("one-to-one") function, in the present example pictured below: | | It is a fact that any old function that you might pick "factors" into a functional composition of two other functions, a surjective ("onto") function and an injective ("one-to-one") function, in the present example pictured below: |
| | | |
| + | {| align="center" cellpadding="10" style="text-align:center; width:90%" |
| + | | |
| <pre> | | <pre> |
− | Source X = {1, 2, 3, 4, 5}
| + | o---------------------------------------o |
− | | o o o o o
| + | | | |
− | g | \ | / \ /
| + | | Source X = {1, 2, 3, 4, 5} | |
− | v \|/ \ /
| + | | | o o o o o | |
− | Medium M = { b , e }
| + | | g | \ | / \ / | |
− | | | |
| + | | v \|/ \ / | |
− | h | | |
| + | | Middle M = { b , e } | |
− | v o o o o o o
| + | | | | | | |
− | Target Y = {A, B, C, D, E, F}
| + | | h | | | | |
| + | | v o o o o o o | |
| + | | Target Y = {A, B, C, D, E, F} | |
| + | | | |
| + | o---------------------------------------o |
| </pre> | | </pre> |
| + | |} |
| | | |
| Writing functional compositions <math>f = g \circ h</math> "on the right", we have the following data about the situation: | | Writing functional compositions <math>f = g \circ h</math> "on the right", we have the following data about the situation: |