There are 7 people numbered as 1 to 7.

The number denotes their height.

Arrange them in a line in such a manner so that the line appears in alternative of their heights, I.e. one short then long, again short then long.

The condition is that, if one by one member(remove 1, then 2, then 3) from the line is omitted, the order of their height remains alternative.

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