let i be Nat; :: thesis: for D being non empty set
for p being Element of D
for f being FinSequence of D st p in rng f & p .. f <= i & i <= len f holds
f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f))

let D be non empty set ; :: thesis: for p being Element of D
for f being FinSequence of D st p in rng f & p .. f <= i & i <= len f holds
f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f))

let p be Element of D; :: thesis: for f being FinSequence of D st p in rng f & p .. f <= i & i <= len f holds
f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f))

let f be FinSequence of D; :: thesis: ( p in rng f & p .. f <= i & i <= len f implies f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f)) )
assume that
A1: p in rng f and
A2: p .. f <= i and
A3: i <= len f ; :: thesis: f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f))
A4: 1 + (p .. f) <= i + 1 by ;
i + 1 <= (len f) + 1 by ;
then ( i <= i + 1 & (i + 1) - (p .. f) <= ((len f) + 1) - (p .. f) ) by ;
then (i + 1) -' (p .. f) <= ((len f) - (p .. f)) + 1 by ;
then A5: (i + 1) -' (p .. f) <= len (f :- p) by ;
(((i + 1) -' (p .. f)) -' 1) + (p .. f) = (((i -' (p .. f)) + 1) -' 1) + (p .. f) by
.= (i -' (p .. f)) + (p .. f) by NAT_D:34
.= i by ;
hence f /. i = (Rotate (f,p)) /. ((i + 1) -' (p .. f)) by ; :: thesis: verum