lingxing

set K {               }
set T ABCDEFGHIJKLMOPQL
set Z [ expr [ string length $T ]/2]
for { set a $Z } { $a >= 0 } { incr a -1 } {
    set B [ string range $K 0 $a-1 ]
    set L [ string range $T 0 [expr ($Z-$a)*2] ]
    puts [append B $L]
}
for { set B 1 } { $Z >= $B } { incr B } {
    set S [ string range $K 0 $B-1 ]
    set A [ string range $T 0 [expr ($Z-$B)*2] ]
    puts [append S $A]
}