covariant hom-functor preserves small limits

1. Proposition

2. Proof

Let 20231017-hom_functor_preserves_limits_68c2e4f467e25e7fe0a812a64e0b6a3501aa2e53.svg be a diagram

20231017-hom_functor_preserves_limits_4e17fe9ade25bbe24ae59197ad62cfde0f161d34.svg

then consider for 20231017-hom_functor_preserves_limits_770b56b74da17dfa540a3e9e4cbc2958b00d5c04.svg the diagram

20231017-hom_functor_preserves_limits_8b1e32e7c80258ad4cb61996890997006c1c8dcd.svg

Suppose 20231017-hom_functor_preserves_limits_a5ca1e1e9495f4799a571f0308c9e1ed89eec7a0.svg is a set with morphism

20231017-hom_functor_preserves_limits_23328c555eb87eec39ea6dfa09c91dde621902c1.svg
20231017-hom_functor_preserves_limits_f1c4463b18b4fb81a1eb87ee0731efa167d3e358.svg

Then each 20231017-hom_functor_preserves_limits_65f586b80072fca213ecb6dd3da6e741ff30441b.svg defines morphismss

20231017-hom_functor_preserves_limits_9920462160ada55eb7a4ac275e771bfe89be9db0.svg

where by assumption

20231017-hom_functor_preserves_limits_5e2d8c1e2b2355a5f7113515a62d5c7cce040f35.svg

Thus by universal property, there exists a unique morphism 20231017-hom_functor_preserves_limits_37e83f7de125c1861b633294434e239e948ad549.svg

20231017-hom_functor_preserves_limits_34ccf26ba321ceae1baa9b2718105d5eddf3503e.svg

Thus let

20231017-hom_functor_preserves_limits_79b002d7472336234b5115f89491934253ec7a99.svg
20231017-hom_functor_preserves_limits_7bcde667cd57af88902b2255a36777d18c444310.svg

Then this respects the diagram, as

20231017-hom_functor_preserves_limits_92eccfd6ec0e6e0a7b187a7b4987d4b2cd88aee7.svg

Furthermore suppose there exists a map 20231017-hom_functor_preserves_limits_95299ec08c6261b8a2ad207716a54be17f45a8f3.svg making the diagram commute. Then for each 20231017-hom_functor_preserves_limits_65f586b80072fca213ecb6dd3da6e741ff30441b.svg it follows, that

20231017-hom_functor_preserves_limits_828566a8f2ec2f6a52fd76fb20ada854bb037e3a.svg

makes the diagram commute and thus by uniqueness of 20231017-hom_functor_preserves_limits_9147560048c5a0fb22f03005b96d6b66d767ce6c.svg, it follows, that

20231017-hom_functor_preserves_limits_f0015c523bf21ff71a9fe7c16faf010f09e440ba.svg

or

20231017-hom_functor_preserves_limits_f89b0bd927bea1071a4f4d94f81c11a3296e1066.svg

Date: nil

Author: Anton Zakrewski

Created: 2024-10-13 So 18:40