RewriteEngine On
RewriteBase /

RewriteCond %{REQUEST_URI} !^/p/
RewriteRule ^__(/.*)?$ /p/ [R=301,L]

RewriteCond %{REQUEST_URI} !^/p/
RewriteRule ^_(/.*)?$ /p/ [R=301,L]

RewriteCond %{REQUEST_URI} !^/p/ 
RewriteRule ^_(/.*)?$ /p/src/ [R=301,L]