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def definition def or abbrev

mulPos

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formal statement (Lean)

 105def mulPos (I J : Interval) (hI : 0 < I.lo) (hJ : 0 < J.lo) : Interval where
 106  lo := I.lo * J.lo

proof body

Definition body.

 107  hi := I.hi * J.hi
 108  valid := by
 109    apply mul_le_mul I.valid J.valid
 110    · exact le_of_lt hJ
 111    · linarith [I.valid]
 112

used by (17)

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depends on (2)

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