(Pre)images of intervals #
In this file we prove a bunch of trivial lemmas like “if we add a to all points of [b, c],
then we get [a + b, a + c]”. For the functions x ↦ x ± a, x ↦ a ± x, and x ↦ -x we prove
lemmas about preimages and images of all intervals. We also prove a few lemmas about images under
x ↦ a * x, x ↦ x * a and x ↦ x⁻¹.
Binary pointwise operations #
Note that the subset operations below only cover the cases with the largest possible intervals on
the LHS: to conclude that Ioo a b * Ioo c d ⊆ Ioo (a * c) (c * d), you can use monotonicity of *
and Set.Ico_mul_Ioc_subset.
TODO: repeat these lemmas for the generality of mul_le_mul (which assumes nonnegativity), which
the unprimed names have been reserved for
Preimages under x ↦ a + x #
Preimages under x ↦ x + a #
Preimages under x ↦ -x #
Preimages under x ↦ x - a #
Preimages under x ↦ a - x #
Images under x ↦ a + x #
Images under x ↦ x + a #
Images under x ↦ -x #
Images under x ↦ a - x #
Images under x ↦ x - a #
Bijections #
If [c, d] is a subinterval of [a, b], then the distance between c and d is less than or
equal to that of a and b
If c ∈ [a, b], then the distance between a and c is less than or equal to
that of a and b
If x ∈ [a, b], then the distance between c and b is less than or equal to
that of a and b
Multiplication and inverse in a field #
The (pre)image under inv of Ioo 0 a is Ioi a⁻¹.