Benchmark: computing 6! + 3^7 = 2907

    version time  speedup   description
    ----------------------------------------------------------
    cbn-2   29.3      1	    rembember reductions (implemented)
    cbn-3   12.1      2.4   parallel substitution
    cbn-4	    	    appView by default (no win, but simplifies lazy implementation)
    cbn-5   10.9      2.7   don't splitAt (length xs) xs
    cbn-6    6.5      4.5   case compilation
    cbn-7    4.7      6	    integer names (implemented)

    lazy-2   3.0     10	    lazy evaluation (STRefs)
    lazy-3   0.27   108	    apps e [] = return e
    lazy-4		    -- bad
    lazy-5   0.08   inf	    add closedness annotation
    lazy-6		    -- no improvement