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### 4.13 Incomplete Objects

When ( or [ is typed to begin entering a complex number or vector, respectively, the effect is to push an incomplete complex number or vector onto the stack. The , key adds the value(s) at the top of the stack onto the current incomplete object. The ) and ] keys “close” the incomplete object after adding any values on the top of the stack in front of the incomplete object.

As a result, the sequence of keystrokes [ 2 , 3 <RET> 2 * , 9 ] pushes the vector ‘[2, 6, 9]’ onto the stack. Likewise, ( 1 , 2 Q ) pushes the complex number ‘(1, 1.414)’ (approximately).

If several values lie on the stack in front of the incomplete object, all are collected and appended to the object. Thus the , key is redundant: [ 2 <RET> 3 <RET> 2 * 9 ]. Some people prefer the equivalent <SPC> key to <RET>.

As a special case, typing , immediately after (, [, or , adds a zero or duplicates the preceding value in the list being formed. Typing <DEL> during incomplete entry removes the last item from the list.

The ; key is used in the same way as , to create polar complex numbers: ( 1 ; 2 ). When entering a vector, ; is useful for creating a matrix. In particular, [ [ 1 , 2 ; 3 , 4 ; 5 , 6 ] ] is equivalent to [ [ 1 , 2 ] , [ 3 , 4 ] , [ 5 , 6 ] ].

Incomplete entry is also used to enter intervals. For example, [ 2 .. 4 ) enters a semi-open interval. Note that when you type the first period, it will be interpreted as a decimal point, but when you type a second period immediately afterward, it is re-interpreted as part of the interval symbol. Typing .. corresponds to executing the `calc-dots` command.

If you find incomplete entry distracting, you may wish to enter vectors and complex numbers as algebraic formulas by pressing the apostrophe key.