If you want to prohibit certain items from occurring together within a portfolio, use the Prohibitions feature located at the bottom of the settings panel.
Add a new prohibition, and select two or more items. These items will not occur all together in the same portfolio the next time you update your analysis.
However, a subset of the items in a prohibition may occur in a portfolio. For example if items 11, 12, and 13 are not to occur within the same portfolio, only portfolios containing ALL three of these items would be prohibited. A portfolio containing two of these items (e.g. 11 and 12) is allowed.
To exclude a single item from occurring within any portfolio, open the Items list and deselect it.