Finding the index of an element:

index ( obj seq -- n )

index-from ( obj i seq -- n )

last-index ( obj seq -- n )

last-index-from ( obj i seq -- n )

Finding the start of a subsequence:

subseq-start ( subseq seq -- i/f )

subseq-start-from ( subseq seq n -- i/f )

subseq-index ( seq subseq -- i/f )

subseq-index-from ( n seq subseq -- i/f )

subseq-starts-at? ( i seq subseq -- ? )

Finding the index of an element satisfying a predicate:

find ( ... seq quot: ( ... elt -- ... ? ) -- ... i elt )

find-from ( ... n seq quot: ( ... elt -- ... ? ) -- ... i elt )

find-last ( ... seq quot: ( ... elt -- ... ? ) -- ... i elt )

find-last-from ( ... n seq quot: ( ... elt -- ... ? ) -- ... i elt )

map-find ( ... seq quot: ( ... elt -- ... result/f ) -- ... result elt )

map-find-last ( ... seq quot: ( ... elt -- ... result/f ) -- ... result elt )