Less than
 Main article: Comparison function
<

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
References
 ↑ Last, Phil. "Boolean Reductions". Vector Journal volume 26, number 1. 201309.
APL builtins [edit]  

Primitive functions  
Scalar  
Monadic  Conjugate ∙ Negate ∙ Signum ∙ Not ∙ Roll ∙ Type  
Dyadic  Add ∙ Subtract ∙ Equal to (Xnor) ∙ Not Equal to (Xor) ∙ Minimum ∙ Maximum ∙ Comparison functions  
NonScalar  
Structural  Shape ∙ Reshape ∙ Tally ∙ Depth ∙ Ravel ∙ Reverse ∙ Raze ∙ Mix ∙ Cut (K) ∙ Pair ∙ Replicate ∙ Partitioned Enclose  
Selection  Take ∙ Drop ∙ Unique ∙ Identity ∙ Select  
Selector  Index generator ∙ Interval Index ∙ Indices  
Computational  Match ∙ Not Match ∙ Nub Sieve ∙ Format ∙ Execute  
Primitive operators  Monadic  Each ∙ Replicate  
Dyadic  Reverse Compose  
Quad names  
Arrays  Index origin ∙ Migration level  
Functions  
Operators  
Other  Zilde ∙ High minus ∙ Function axis 