Less than
 Main article: Comparison function
 For the set function, see Without.
<

Less than (<
) is a comparison function which tests whether the left argument is tolerantly less than and not equal to the right argument, returning 1 if this is the case and 0 otherwise. It is the negation of Greater than or Equal to (≥
). Lessthan Scan, which leaves only the first 1 in a Boolean vector set^{[1]}, is a notable pattern.
Boolean function
When the arguments to Less than are Boolean, it is the converse nonimplication Boolean function:
<
0
1
0
0
1
1
0
0
It returns 1 only if the left argument is 0 and the right argument is 1, and is identical to Residue. Considered as a logical operation, it can be read as isn't, as opposed to.
Lessthan Scan on a Boolean vector returns a vector which indicates the position of the first 1 in the argument, if any:
<\ 0 0 1 0 0 0 1 0
0 0 1 0 0 0 0 0
It is idiom 348, "First one", in the FinnAPL idiom library.
External links
Documentation
 Dyalog
 APLX
 J Dictionary, NuVoc
 BQN
References
 ↑ Last, Phil. "Boolean Reductions". Vector Journal volume 26, number 1. 201309.