 : last2 ( seq -- penultimate ultimate ) 2 tail* first2 ;
 
 ! Due to the way adjusted-tail-slice works, the first element of
-! pairs is <= min, and if the first is < min, then the second is
-! > min. Otherwise the first one would be = min.
-: left-cut ( min pairs -- seq )
+! pairs is <= xmin, and if the first is < xmin, then the second is
+! > xmin. Otherwise the first one would be = xmin.
+: left-cut-x ( xmin pairs -- seq )
     2dup first x < [
         [ dupd first2 y-at 2array ] keep rest-slice swap prefix
     ] [

! If the line spans beyond min or max, make sure there are points
! with x = min and x = max in seq.
: min-max-cut ( min,max pairs -- seq )
    [ first2 ] dip right-cut left-cut ;

: clip-by-x ( min,max pairs -- pairs' )
    2dup x-in-bounds? [

    ] if ;

! Due to the way adjusted-head-slice works, the last element of
! pairs is >= xmax, and if the last is > xmax, then the second to
! last is < xmax. Otherwise the last one would be = xmax.
: right-cut-x ( xmax pairs -- seq )
    2dup last x < [
        [ dupd last2 y-at 2array ] keep but-last-slice swap suffix
    ] [
