The phrase "a third assumption is" is correct and usable in written English.
You can use it when introducing a third assumption in a list of assumptions or arguments in a discussion or analysis.
Example: "In our analysis of the data, a third assumption is that the sample size is representative of the larger population."
Alternatives: "the third assumption states" or "one more assumption is".
A third assumption was that one function of workspace neurons may be to support related processing in more local systems [8] [10].
A second assumption is potentially even more misleading.
A second assumption is that the financial sector will accept the new arrangements in perpetuity.
A second assumption is that all effects that match the global signal are of no interest and can be removed.
A second assumption is that it is safe to cut alfalfa if there are less than 200 GDD (base5 C) remaining before the first killing frost, as there would be insufficient regrowth to use up enough storage carbohydrates to negatively affect alfalfa persistence.
A fourth assumption is that human nature is intensely social.
A second assumption is about the light properties, which is supposed to be perfectly diffused, since the sun is far enough to be considered as an illumination source situated at infinite distance.
However, notice that conditions (PM1 - PM4) only refer to the interval ([ 0,infty ) ). In the field of fixed point theory, a fifth assumption is usually considered. (PM5): (lim_{trightarrowinfty}F_{xy}(t)=1) for all (x,yin X). (lim_{trightarrowinfty}F_{xy}(t)=1) for all (x,yin X). A discussion about the necessity of this condition can be found in [19].
However, notice that conditions (PM1 - PM4) only refer to the interval ([ 0,infty ) ). (2) In the field of fixed point theory, a fifth assumption is usually considered. (PM5): (lim_{trightarrowinfty}F_{xy}(t)=1) for all (x,yin X). A discussion about the necessity of this condition can be found in [19].
