learn rules: .=>

 .=> :
    description:
        op |ket> .=> sequence
        sequence-append the sequence on the right hand side to the existing definition of op|ket>
        if initially op|ket> is not defined, then just set it to the sequence
        useful for piece by piece construction of a sequence
        if the right hand side is a general sequence, it will be compiled to a sequence before being appended to op|ket>

    examples:
        -- learn a sequence one ket at a time:
        list-of |primes> .=> |2>
        list-of |primes> .=> |3>
        list-of |primes> .=> |5>
        list-of |primes> .=> |7>
        list-of |primes> .=> |11>
        list-of |primes> .=> |13>
        list-of |primes> .=> |17>
        list-of |primes> .=> |19>

        -- now see the full sequence:
        sa: list-of |primes>
            |2> . |3> . |5> . |7> . |11> . |13> . |17> . |19>

    see also:
        seq-learn, => , .=> , #=> , !=>