After Dyalog adopted the definition of Replicate used by NARS, APL2 developed another definition, which differs in its handling of negative numbers in the left argument. In APL2, a negative number does not "consume" an element of the right argument, so that instead of (≢⍺)=≢⍵, we have (+/0≤⍺)=≢⍵. Developers of XAPL noticed that both extensions can be supported simultaneously: if the left argument has any negative numbers, the interpreter can tell which one the programmer meant by checking whether the right argument's length is equal to the left (NARS-style) or shorter (APL2-style). In fact, APLX already does this:
```
APLX for Windows
Copyright (C) 2001-2010 MicroAPL Ltd
WS Size = 20.0MB, Version = 5.1.0
CLEAR WS
1 ¯2 3 2 / 10 20 30
10 0 0 20 20 20 30 30
¯2 3 2 / 10 20 30
0 0 20 20 20 30 30
```