Ups,
I forgot to mention things like
+('a0',,'e3') == +( <a0 a1 a2 a3>,
<b0 b1 b2 b3>,
<c0 c1 c2 c3>,
<d0 d1 d2 d3>,
<e0 e1 e2 e3> )
== +( 'a0','a1','a2','a3',
'b0','b1','b2','b3',
'c0','c1','c2','c3',
'd0','d1','d2','d3',
'e0','e1','e2','e3' )
== 20
+('a0';;'e3') == +( <a0 a1 a2 a3>;
<b0 b1 b2 b3>;
<c0 c1 c2 c3>;
<d0 d1 d2 d3>;
<e0 e1 e2 e3> )
== +( 'a0','a1','a2','a3';
'b0','b1','b2','b3';
'c0','c1','c2','c3';
'd0','d1','d2','d3';
'e0','e1','e2','e3' )
== 5 * 4 == 20 # == (4,4,4,4,4) ?
[+]('a0';;'e3') == +('a0','a1','a2','a3') +
+('b0','b1','b2','b3') +
+('c0','c1','c2','c3') +
+('d0','d1','d2','d3') +
+('e0','e1','e2','e3')
== [+](4,4,4,4,4) == 5 * 4 == 20
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