Paste: don't understand this error

(scratchpad) : <seq1> ( -- seq ) { 1 2 3 } ;
(scratchpad) : <seq2> ( -- seq ) { 4 5 6 } ;
(scratchpad) <seq1> seq-min .
1
(scratchpad) <seq2> seq-min . 
4
(scratchpad) { { 1 2 3 } { 4 5 6 } } [ seq-min ] map .
{ 1 4 }


So far so good!  But...

(scratchpad) { <seq1> <seq2> } [ seq-min] map
"Generic word length does not define a method for the word class.  Dispatching on object <seq1>"