let i be Integer; :: thesis: for f being FinSequence st 1 <= i & i <= len f holds
i in dom f
let f be FinSequence; :: thesis: ( 1 <= i & i <= len f implies i in dom f )
assume that
A1: 1 <= i and
A2: i <= len f ; :: thesis: i in dom f
i is Element of NAT by A1, INT_1:3;
hence i in dom f by A1, A2, FINSEQ_3:25; :: thesis: verum