{ /p deff {
  [ -01 { _ p { } { -- } ? * } each ]
} } /engrep deff

{ engrep * } /grep deff
{ -110 ; engrep |dom -20*1* } /indices deff

{ /p deff _ /a deff len /l defv
  1 neg /r defv

  0 {
    _ l lt 1 neg r eq and
  } {
    _ a p { _ =r } { } ? *
      1 add
  } loop --
  r
} /index deff

[ 1 2 3 4 5 6 7 8 9 ] { 2 mod } grep dump
[ 1 3 4 5 6 7 8 9 ] { 2 mod } indices dump
[ 1 3 4 5 6 7 8 9 ] { 6 eq } index dump
[ 0 0 0 1 0 0 1 1 ] { } indices dump