While both retinol and Retin-A contain retinoids, they differ in their concentration. Retinol and other forms, such as retinal and retinyl palmitate are found in many over-the-counter anti-aging creams. While these all contain a form of vitamin A, the concentration of retinoids is weak. Retin-A is a prescription retinoid and is a brand name for tretinoin, which is the carboxylic acid form of vitamin A and was one of the early topical acne treatments. Retin-A is sold by prescription because its acid composition is much greater than in over-the-counter products.
Undefined is a term used when a mathematical result has no meaning. More precisely, undefined values occur when an expression is evaluated for input values outside of its domain. ( 1 if no complex numbers). ( 2 if no complex numbers). ( 3 units in radians, no complex infinity). ( 4 if no complex infinity).
The term well-defined is also used to indicate whether a logical statement is unambiguous. A function that is not well-defined is not the same as a function that is undefined.For example, if f (x) = 1/ x, then f (0) is undefined, but this has nothing to do with the question of whether f (x) = 1/ x is well-defined. It is; 0 is simply not in the domain of the function.hereas the definition in step 1. is formulated with the freedom of any definition and is certainly effective (without the need to classify it as âwell-definedâ), the assertion in step 2. has to be proved: If and only if, we get a function, and the of definition is well-defined.