English
The fractional-part function on a ring with a floor operation is periodic with period 1; i.e., fract(a + 1) = fract(a).
Русский
Дробная часть на кольце с операцией floor периодична с периодом 1, то есть fract(a + 1) = fract(a).
LaTeX
$$$\operatorname{fract}(a+1) = \operatorname{fract}(a)$$$
Lean4
theorem fract_periodic (α) [Ring α] [LinearOrder α] [IsStrictOrderedRing α] [FloorRing α] :
Function.Periodic Int.fract (1 : α) := fun a => mod_cast Int.fract_add_intCast a 1