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. Less-than Scan, which leaves only the first 1 in a Boolean vector set, is a notable pattern.

Boolean function
When the arguments to Less than are Boolean, it is the converse nonimplication Boolean function:
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! !! !! ! ! 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.
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Less-than Scan on a Boolean vector returns a vector which indicates the position of the first 1 in the argument, if any: It is idiom 348, "First one", in the FinnAPL idiom library.

Documentation

 * Dyalog
 * APLX
 * J Dictionary, NuVoc