kill(all);

two assignments

l : a-h;

h : a - 'l;

in the assignment above, the apostrophe is employed to **inhibit** the evaluation of the l symbol.
in general, the apostrophe is an inhibitor of the implicit evaluation.

l;

'l;

integrate(x , x);

'integrate(x,x) ;

diff(f,x);

'diff(f,x);

'diff(x^3,x);

it does not always work...

'cos(%pi/3);

'diff(x,x);

implicit evaluation alone

l;

single explicit evaluation

ev(l);

twice nested evaluation (or twice repeated)

ev( ev(l));

ev(l,eval);

three times repeated evaluation

ev( ev( ev(l)  ));

ev(l,eval,eval);

not completely equal..

infinite evaluation is recursive

ev(l);
ev(l,eval);
ev(l,eval,eval);
ev(l,eval,eval,eval);
ev(l,eval,eval,eval,eval);

two subsequent evaluations are always different

the following statement, if DONOTREMOVEME is removed, locks maxima in an infinite evaluation loop.

DONOTREMOVEMEev(l,infeval);