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§16.7. Blank entries
We are allowed to leave certain entries blank (perhaps to be filled in later, perhaps not) by writing "--" instead of the relevant value:
|
Element |
Symbol |
Atomic number |
Atomic weight |
|
"Hydrogen" |
"H" |
1 |
1 |
|
"Iron" |
"Fe" |
-- |
56 |
|
"Zinc" |
-- |
30 |
65 |
|
"Uranium" |
"U" |
92 |
238 |
In effect, blank entries don't exist. "--" is not a value, but only a hole where a value might be. It can be useful to check for this:
if there is (a table entry):
This condition is true if the entry referred to exists, that is, that is, the space for it in the table is not blank. Examples:
if there is a symbol corresponding to an atomic number of 30 in the Table of Selected Elements ...
if there is an atomic number in row 2 of the Table of Selected Elements ...
if there is no (a table entry):
This condition is true if the entry referred to does not exist, that is, the space for it in the table is blank. Examples:
if there is no symbol corresponding to an atomic number of 30 in the Table of Selected Elements ...
if there is no atomic number in row 2 of the Table of Selected Elements ...
