What is the differnece in meaning between the notstions of a line over QR and not a line over QR?

The difference in meaning between a line over the letters "QR" and no line over "QR" is related to the mathematical concept of negation. When a line (referred to as a strikeout line or bar) is placed over a statement or symbol, it usually represents the concept of negation or logical negation.

If you see a line over the letters "QR" (e.g., ̶QR), it typically indicates that the statement "QR" or the symbol QR is being negated or is false. In other words, the line over "QR" would imply the opposite or the negation of whatever statement or property "QR" represents.

On the other hand, if there is no line over "QR," it generally means that the statement or symbol "QR" is true or not negated. In this case, you would consider "QR" as a positive or non-negated statement.

To understand the context and meaning precisely, it is essential to know the specific discipline or framework in which the notation is being used, as different fields might have slightly different conventions regarding the use of notation.