(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
.