+
+ @ibs or confess 'internal error, expected anchor at least ?';
+
+ my $ib;
+ my $ibleaf;
+ foreach my $tibix (0..$#ibs) {
+ my $tib = $ibs[$tibix];
+ my $ff = is_fast_fwd $bwb, $tib;
+ my $ok = !$ff ? 'rej' : $ib ? 'extra' : 'ok';
+ my $tibleaf = "interchange-mbcand-$ok-$tibix";
+ $mwrecknote->($tibleaf, $tib);
+ next unless $ff;
+ next if $ib;
+ $ib = $tib;
+ $ibleaf = $tibleaf;
+ }
+
+ $ib or $nomerge->("no suitable interchange merge base");