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I made this just to make it blue
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Find an order theory book, also I think that huge category theory PDF (Harold Simmons) has it


A map, [ilmath]f:X\rightarrow Y[/ilmath] between two posets, [ilmath](X,\sqsubseteq)[/ilmath] and [ilmath](Y,\preceq)[/ilmath] is monotonic or monotone if:

  • [ilmath]\forall a,b\in X[a\sqsubseteq b\implies f(a)\preceq f(b)][/ilmath], or in words:
    • It preserves the ordering.

For a sequence

Recall that a sequence, [ilmath] ({ A_n })_{ n = 1 }^{ \infty }\subseteq X [/ilmath] (for some poset, [ilmath](X,\sqsubseteq)[/ilmath]) can be considered as a mapping:

  • [ilmath]A:\mathbb{N}\rightarrow X[/ilmath] given by [ilmath]A:n\mapsto A_n[/ilmath]

We can now apply the above definition directly.

Work needed

TODO: These

  1. How can we have monotonically decreasing things? Via the dual partial ordering of course! To have [ilmath]\le[/ilmath] is to induce a unique [ilmath]\ge[/ilmath] - these are distinct orderings.
  2. Not sure, but probably some call this isotonic, while monotonic is either increasing or decreasing.
  3. Unite with monotonic set function