. exact tsub_lt_self xpos zero_lt_one
case k.h₁
n x : ℕ
npos : 0 < n
xpos : 0 < trunc n x
⊢ trunc n x - 1 < trunc n x

case k.h₂
n x : ℕ
npos : 0 < n
xpos : 0 < trunc n x
⊢ ulp n (trunc n x - 1) ≤ ulp n (trunc n x)
case k.h₂
n x : ℕ
npos : 0 < n
xpos : 0 < trunc n x
⊢ ulp n (trunc n x - 1) ≤ ulp n (trunc n x)