 expression at the right immediately
and assigns its value to the parameter. The second form assigns the value
by evaluating  the expression at right every time the parameter is
actually used.
This holds as well for element parameters - beware ! If you want to modify
e.g. the strength of a quadrupole later (e.g. in a match, 
or by entering a new value for a parameter on which it depends)
then the defition has to be
<pre>
qd:quadrupole,k1:= ak1;
</pre>
and not
<pre>
qd:quadrupole,k1 = ak1;
</pre>
In the latt