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Haskell has "elem" predicate to tell like:
Prelude> 5 `elem` [2,4..10]
False
In F#, how to conveniently tell whether a value is in a list, or array, or seq or map, or dictionary?
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f, f′ and f″ Since (f′)′=f″, when f′ is increasing, f″ is positive. Similarly, when the slopes of tangent lines are decreasing, i.e. when f′ is decreasing, the function is concave down, as you can see in the second two graphs below. Since (f′)′=f″, when f′ is decreasing, f″ is negative.
The ∘ symbol denotes a composite function - it looks similar to the multiplication symbol, ⋅, but does not mean the same thing. (f ∘ g)(x) is the same thing as f(g(x)). (f ∘ g)(x) is not the same thing as (g ∘ f)(x). (g ∘ f)(x) is the same thing as g(f(x)), which will often be different than f(g(x)).
A maplet or maplet arrow (symbol: ↦, commonly pronounced "maps to") is a symbol consisting of a vertical line with a rightward-facing arrow. It is used in mathematics and in computer science to denote functions (the expression x ↦ y is also called a maplet).
In F# it is
List.contains <element> <list>
Example:
List.contains 5 [2..2..10]
-->
val it : bool = false
contains is also defined for the other container types.
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